1. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 1 Supported by Office of Science S.A. Sabbagh 1, R. E. Bell 2, J.E. Menard 2, D.A. Gates 2, A.C. Sontag 1, J.M. Bialek 1, B.P. LeBlanc 2, F. Levinton 3, K. Tritz 4, H. Yu 3, and the NSTX Research Team Resistive Wall Mode Active Stabilization in High Beta, Low Rotation Plasmas Columbia U Comp-X General Atomics INEL Johns Hopkins U LANL LLNL Lodestar MIT Nova Photonics NYU ORNL PPPL PSI SNL UC Davis UC Irvine UCLA UCSD U Maryland U New Mexico U Rochester U Washington U Wisconsin Culham Sci Ctr Hiroshima U HIST Kyushu Tokai U Niigata U Tsukuba U U Tokyo JAERI Ioffe Inst TRINITI KBSI KAIST ENEA, Frascati CEA, Cadarache IPP, Jülich IPP, Garching U Quebec 21 st IAEA Fusion Energy Conference 16 – 21 October, 2006 Chengdu, China 1 Department of Applied Physics, Columbia University, New York, NY, USA 2 Plasma Physics Laboratory, Princeton University, Princeton, NJ, USA 3 Nova Photonics, Inc., Princeton, NJ, USA 4 Johns Hopkins University, Baltimore, MD, USA v1.0

2. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 2 Experiments in 2006 examined RWM physics and stabilization at ITER-relevant rotation  RWM active stabilization  New control system installed  RWM control demonstrated  RWM actively stabilized in slowly rotating plasmas  Plasma rotation control  Sustained rotation by real- time reduction of amplified error field  Reduced rotation by non- resonant magnetic braking Passive plates Blanket modules Port Control Coils ITER vessel ITER plasma boundary 012 R(m) Z(m) 0 -2 1 2 NSTX / ITER RWM control Advantage: low aspect ratio, high  provides high leverage to uncover key tokamak physics for ITER (e.g. RWM control, momentum dissipation)

3. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 3 2.01.51.00.50.0 R (m) -2 0 1 2 120047 t = 0.745s B ru B pu B r ext n = 1 B rl B pl control coils Z (m) stabilizer plates  Stabilizer plates for kink mode stabilization  External midplane control coil closely coupled to vacuum vessel  Similar to ITER port plug designs  Internal sensors can detect n = 1 – 3 RWM  Unstable n = 1 – 3 RWMs already observed in NSTX (Sabbagh, et al., NF 46 (2006) 635.)  n > 1 RWM studied during n = 1active stabilization RWM Active Feedback System Installed on NSTX

4. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 4 Dynamic error field correction (DEFC) increases pulse length in strongly rotating plasmas No-wall limit Rotating mode onset control off open-loop Open+closed loop  Open-loop control of error field amplified by stable RWM  yields higher rotation  yields longer pulse  Combination of open + closed loop control yielded best result  Rotation increase or saturation at long pulse lengths - first time in NSTX see OV/2-4 Menard

5. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 5 RWM stabilized at ITER-relevant rotation for ~ 90/  RWM  First such demonstration in low A tokamak  Exceeds DCON  N no-wall for n = 1 and n = 2  n = 2 RWM amplitude increases, mode remains stable while n = 1 stabilized Multi-mode research – connection to RWM stabilization in RFPs (Sabbagh, et al., PRL 97 (2006) 045004.) NN I A (kA)  B pu n=1 (G)  B pu n=2 (G)   /2  (kHz)  N >  N (n=1) no-wall 120047 120712   <  crit 92 x (1/  RWM ) 6 4 2 0 8 4 0 1.5 1.0 0.5 0.0 20 10 0 20 10 0 t(s) 0.40.50.60.70.80.9

6. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 6 RWM stabilized at ITER-relevant rotation for ~ 90/  RWM  First such demonstration in low A tokamak  Exceeds DCON  N no-wall for n = 1 and n = 2  n = 2 RWM amplitude increases, mode remains stable while n = 1 stabilized Multi-mode research – connection to RWM stabilization in RFPs  n = 2 internal plasma mode seen in some cases (Sabbagh, et al., PRL 97 (2006) 045004.) t(s) 0.40.50.60.70.80.9 NN I A (kA)  B pu n=1 (G)  B pu n=2 (G)   /2  (kHz)  N >  N (n=1) no-wall 120047 120712   <  crit 92 x (1/  RWM ) 120717 6 4 2 0 8 4 0 1.5 1.0 0.5 0.0 20 10 0 20 10 0

7. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 7 RWM stabilized at ITER-relevant rotation for ~ 90/  RWM  First such demonstration in low A tokamak  Exceeds DCON  N no-wall for n = 1 and n = 2  n = 2 RWM amplitude increases, mode remains stable while n = 1 stabilized Multi-mode research – connection to RWM stabilization in RFPs  n = 2 internal plasma mode seen in some cases  Plasma rotation   reduced by non-resonant n = 3 magnetic braking  Non-resonant braking to accurately determine RWM critical rotation (Sabbagh, et al., PRL 97 (2006) 045004.) t(s) 0.40.50.60.70.80.9 NN I A (kA)  B pu n=1 (G)  B pu n=2 (G)   /2  (kHz)  N >  N (n=1) no-wall 120047 120712   <  crit 92 x (1/  RWM ) 120717 6 4 2 0 8 4 0 1.5 1.0 0.5 0.0 20 10 0 20 10 0

8. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 8 /A/A passively stabilized by rotation (120038, t = 0.535s) experimental critical rotation profile (120712, t = 0.575s) actively stabilized (120047 t = 0.825s) R (m)  crit /  A (axis) (q=2) Rotation reduced far below RWM critical rotation profile  Rotation typically fast and sufficient for RWM passive stabilization  Reached   /  A = 0.48| axis  Non-resonant n = 3 magnetic braking used to slow entire profile  The   /  crit = 0.2| q = 2  The   /  crit = 0.3| axis  Less than ½ of ITER Advanced Scenario 4   /  crit (Liu, et al., NF 45 (2005) 1131.)  Rotation profile responsible for passive stabilization, not just single radial location  see paper EX/7-2Rb Sontag (120717, t = 0.915s)

9. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 9 0.91.11.31.5 R (m) T NTV (N m) Observed rotation decrease follows NTV theory 3 4 2 1 0 measured theory t = 0.360s 116931 axis n = 3 applied field configuration  First quantitative agreement using full neoclassical toroidal viscosity theory (NTV)  Due to plasma flow through non-axisymmetric field  Computed using experimental equilibria  Trapped particle effects, 3-D field spectrum important  Viable physics for simulations of plasma rotation in future devices (ITER, CTF, KSTAR)  Scales as  B 2 (T i / i )(1/A) 1.5  Low i ITER plasmas will have higher rotation damping (Zhu, et al., PRL 96 (2006) 225002.) see EX/7-2Rb Sontag

10. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 10 45 o (119761) 315 o (119755) 290 o (119764) 225 o (119770) negative feedback response  f 6 4 2 0 8 6 4 2 0 30 20 10 0 NN   /2  ( kHz )  B pu n=1 (G) 0.50.40.60.70.80.9 t (s) feedback on  RWM active feedback on n = 1  Control current relative phase,  f  Phase scan shows superior settings for negative feedback  Pulse length increases  Internal plasma mode seen at  f = 225, damped feedback system response  Gain scan also performed  Sufficiently high gain showed feedback loop instability Varying relative phase shows positive/negative feedback

11. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 11  Poloidal n =1 RWM field decreases to near zero  Radial RWM field increasing  Subsequent growth of poloidal RWM field  Asymmetric above/below midplane  Midplane radial sensor shows RWM bulging  Upper/lower radial sensors show decrease, while midplane sensor increases  Theory: may be due to stable ideal n = 1 modes becoming less stable (e.g. q evolution) RWM may change form and grow during active control 0.590.550.630.670.710.75 t (s) 6 4 2 0 8 4 0 20 10 0 4 2 0 6 4 2 0 NN   /2  ( kHz )  B pu,l n=1 (G)  B ru,l n=1 (G)  B r ext n=1 (G)  N collapse 120048 bulge Future research will assess using combined sensors for optimization   =  crit

12. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 12 Clear differences between RWM and internal plasma mode No active stabilization (RWM disrupts plasma) Active stabilization (fast  N drop, plasma recovers) 0.560.600.640.68 20 40 0 t(s) 0.5 1.0 1.5 0.0  B p n=1 (G) 20 40 0  B p n=1 (G) USXR (arb) edge core 0.5 1.0 1.5 0.0 USXR (arb) edge core 0.72400.72410.72420.7239 t(s) 0.660.700.740.78 t(s)  Internal mode ~ 25 kHz  Plasma rotation ~ 12 kHz (n = 2) 5 ms 20  s 120717 negative feedback response 120705 (USXR: K. Tritz JHU) mode strongest at edge n = 2 RWM n = 1 n = 2 n = 2 internal mode 0.60.8 20 40 0 t(s) (kHz) n = 1 n = 2

13. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 13 NSTX begins RWM active stabilization research relevant to ITER and beyond  First demonstration of RWM active stabilization in high , low A tokamak plasmas with   significantly less than  crit  In the predicted range of ITER  Plasma response to feedback control demonstrated  Stability of n = 2 RWM demonstrated during n = 1 RWM stabilization  n = 1,2 plasma mode sometimes observed; fast  collapse, recovery  Plasma rotation reduction by non-resonant applied field; follows NTV theory  Full NTV calculation yielding quantitative agreement to experiment  Key component of RWM stability physics and dynamics; general momentum transport relevance

14. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 14 Additional slides for poster follow

15. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 15 Work slides follow

16. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 16 NSTX begins RWM active stabilization research relevant to ITER, KSTAR, CTF Passive stabilizers (IVCC) (top) Passive stabilizers Blanket modules Port Control Coils ITER vessel ITER plasma boundary 012 R(m) Z(m) 0 -2 1 2 NSTXITERKSTAR  KSTAR physics design supported by past design studies, present experiments in NSTX, DIII-D In-Vessel Control Coils

17. NSTX IAEA FEC 2006 PD: S.A. Sabbagh 17 Close connection to present experiments in NSTX impacts the KSTAR stability physics study  RWM active stabilization demonstrated in low rotation (ITER-relevant) plasmas (Sabbagh, et al., PRL 97 (2006) 045004)  KSTAR with co-NBI should have rotation control for experiments  Precise plasma rotation control through neoclassical toroidal viscosity (Zhu, et al., PRL 96 (2006) 225002)  n = 2 non-resonant magnetic braking possible rotation control option for KSTAR  Unstable resistive wall mode with toroidal mode number n > 1 observed (Sabbagh, et al., NF 46 (2006) 635)  May need to address n > 1 unstable modes in KSTAR at the highest beta or for certain equilibrium profile shapes  RWM critical rotation speed (H. Reimerdes, et al., PoP 13 (2006) 056107)  Dependence on aspect ratio, Alfven speed, ion collisionality – key research topic